1. Field of the Invention
The present invention relates to a method of designing a gear, a method of manufacturing the gear, and the gear manufactured by the manufacturing method, and more particularly, to techniques for efficient and easy designing and manufacturing of gears which have a reduced gear noise.
2. Discussion of the Background
A tooth of a gear ideally has an involute profile, but usually has an error due to heat treatment, for example. The gear may have a transmission error due to the error in the tooth profile, causing a gear noise. Further, misalignment of the axis of one of shafts on which meshing gears are mounted may cause partial contact (edge contact) in which the teeth of one of the gears contact at their edges with the tooth surface of the other gear, resulting in a comparatively large amount of transmission error of the gears. The axial misalignment of the gear shaft, which may be caused by a manufacturing or assembling error of a gear box, consists of an error in parallelism of the gear axis due to deviation from the nominal axis, and an error of torsion about the gear axis. The above-indicated transmission error is an error in the angle of rotation of the pair of meshing gears, which may be represented by an amount of advance or retard of the driven gear when the other gear is rotated at a constant velocity.
On the other hand, since the gear noise depends upon a load, the gear specifications and the tooth surface modifications are generally selected so as to reduce the transmission error (gear noise), by conducting simulations taking account of only the gear deflection due to the load, or by conducting tests on prototype gears under various conditions. However, a mechanism in which the load has an influence on the transmission error has not been clarified, and the influence cannot be exactly calculated. Therefore, it has been required to conduct such simulations or prototype tests over the entire range of the load in which the gears are used.
It is also proposed to design a gear, by using a contact ratio thereof which is determined on the assumption that the gear has no errors or tooth surface modification. However, since the amount of transmission error (gear noise) differs depending upon the specific method of the tooth surface modification, for instance, simulations or tests on prototype gears must also be effected under various conditions to determine the gear specifications or tooth surface modifications.
However, such simulations or prototype tests require extremely long time of calculation, large amount of cost for the manufacture of the prototypes and large number of evaluation steps. The probability of obtaining an optimum solution depends upon the number of the simulations or tests conducted, and a limited number of the simulations or tests does not necessarily provide a completely satisfactory gear.